The invention relates to a drive device for lifting a vehicle engine hood adapted to protect pedestrians, in particular a motor vehicle engine hood.
Raising the engine hood of a motor vehicle with the aid of a drive device, if necessary via a lifting gear, to form a wedge for the protection of pedestrians, is known from the prior art. It is necessary in this regard to provide the force conveyed by the drive device in an effective manner so that the engine hood is swiftly raised.
The object of the invention is to provide a drive device for lifting a vehicle engine hood, in particular the engine hood of a motor vehicle, for the protection of pedestrians, said drive device delivering the force which is necessary for the drive motion into the mountings of the drive device in a torque-free manner, at least at the beginning of the drive motion.
This object is achieved by the drive device specified in claim 1.
This drive device includes a pressure pipe in which a piston which can be driven by a drive gas can be moved along a linear guideway, A piston rod is connected to the piston, the piston rod having a rod portion projecting beyond a first guideway end of the pressure pipe. A connection point to be connected force-lockingly to a lifting gear for the engine hood is provided at this projecting rod portion. This connection point is preferably provided in the form of a receiver for a part of the lifting gear. Another connection point is provided at the second guideway end located opposite the first guideway end, said connection point being adapted for force-locking support of the pressure pipe on the vehicle body. This support is preferably provided at a motor vehicle part located underneath the engine hood.
The two connection points are arranged at the pressure pipe in line with the linear guideway of the piston. Owing to this arrangement of the two connection points in linear alignment with the guideway of the piston, the forces applied by the drive device to the drive gear of the engine hood are delivered torque-free when the piston is driven, at least at the beginning of the drive motion. The drive gas for the piston is supplied by a gas source disposed in a pressure pipe portion which is at an angle to the linear guideway. The piston is driven along the linear guideway in the pressure pipe by the drive gas discharged from the gas source, and the driving force is transferred via the piston rod and the connection point to the piston rod to raise the engine hood above the connected lifting gear. As already described, the transmission of force to the lifting gear is torque-free, at least at the beginning of the drive motion, due to the connection points being aligned with the linear guideway. The linear drive motion is translated by the lifting gear into the lifting movement of the engine hood.
It is preferable that a stop ring arranged around the piston rod be provided at the front end of the piston in the drive direction. This stop ring may preferably consist of a motion-damping material. In the front end position of the piston being driven, the stop ring is at least motion-damping. For that purpose, it may be made of a deformable material, in particular of an elastic material such as rubber or plastic. The stop ring may be in the form of an O-ring.
The pressure pipe may preferably be rounded at the first guideway end. This rounded portion is located in the region in which the pressure pipe end is in contact with the piston rod. Due to this rounded portion, the piston and the piston rod, which may preferably be of one-piece construction, adopt a slightly tilted position at the end of the drive motion, relative to the linear guideway for the piston in the pressure pipe. The rounded portion of the pressure pipe end prevents the pressure pipe end from cutting into the tilted piston rod. This ensures that the piston and the piston rod can be pressed back into their initial position when the pressure in the work chamber has dropped.
The gas source is preferably designed as an electrically ignitable gas generator. Due to the pressure pipe portion being arranged at an angle to the linear guideway of the pressure pipe, electrical contact with the electrically ignitable gas generator can be made in a simple manner, preferably at the end of the angled pressure pipe portion. A standard electrical plug-type connectors can be used for this purpose. The gas generator may preferably be designed as a pyrotechnical gas generator.
Instead of a plug connection, the gas generator can be electrically contacted by means of a lead wire connection, in which the electrical cable is guided through an at least liquid-tight through hole to the ignition device of the gas generator. The liquid-tight duct is tightly inserted into the end of the angled pressure pipe portion. The other end of the current-carrying cable can be connected at a suitable place in the motor vehicle to the source of current by means of a plug connection.
The electrical contacting point at the end of the angled pressure pipe portion may preferably be surrounded liquid-tightly by a sleeve, so that splash water cannot reach the electrical contacting point when the engine is being washed.
A sealing cap may be provided at the end of the pressure pipe at which the driving force is transferred to the lifting gear. This sealing cap is preferably connected securely by positive engagement to the projecting portion of the piston rod and may be disposed on the pressure pipe end with a press fit that is releasable during piston operation. The interior of the piston is thus protected against entry of liquid, in particular against water, when power washing the engine, since no liquid can pass through the gap between the piston rod and the pressure pipe. When the piston is being driven, the gas in front of the piston, in the drive direction, in particular air, is driven out through the gap between the piston rod and the pressure pipe, as the press fit between the sealing cap and the pressure pipe end is released.
A braking path formed by narrowing the cross-section of the pressure pipe, in particular by conically tapering the walls of the pipe, is preferably provided for the driven piston in front of the first guideway end in the drive direction of the piston. This prevents separation of the individual parts forming the drive device in the event of the gas source being accidentally activated in the uninstalled state, in particular in the event of the gas generator being ignited. Due to the narrowing cross-section of the pressure pipe, the piston is braked over a specific distance in such a way that it cannot escape from the pressure pipe. The cross-sectional narrowing of the pressure pipe may transition continuously into the rounded portion provided at the pressure pipe end.
As already mentioned in the foregoing, the piston and the piston rod are of one-piece construction. In that case, more particularly, the piston and the piston rod may be made of plastic, in particular of a fiber/plastic composite material. In order to meet the temperature requirements, the piston and the piston rod may be provided with a core made of a metal, preferably of steel. The core may be provided with connection apertures with which the plastic material can engage. The core may also be contoured to match the contours of the piston, the piston rod and the connection point.
When assembling the drive device, the piston with the pre-mounted piston rod is disposed inside the pipe through the one open end of the pipe forming the first guideway end. The gas source, in particular the gas generator, is mounted inside the pipe through the end of the angled pressure pipe portion and when an electrically ignitable gas generator is used, the electrical contacts can be provided in a simple manner by means of a plug connection at the end of the angled pressure pipe portion or by a lead wire connected at a suitable position in the vehicle. The ends of the pipe are subsequently rolled or bent.